Path planning and collision avoidance for movement of instruments in a radiation therapy environment

ABSTRACT

Apparatus and methods for therapy delivery are disclosed. In one embodiment, a therapy delivery system includes a plurality of movable components including a radiation therapy nozzle and a patient pod for holding a patient, a patient registration module for determining a desired position of at least one of the plurality of movable components, and a motion control module for coordinating the movement of the least one of the plurality of movable components from a current position to the desired position. The motion control module includes a path planning module for simulating at least one projected trajectory of movement of the least one of the plurality of moveable components from the current position to the desired position.

STATEMENT REGARDING FEDERALLY SPONSORED R&D

This invention was made with United States Government support under theDAMD17-99-1-9477 and DAMD17-02-1-0205 grants awarded by the Departmentof Defense. The Government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are incorporated by reference in their entirety under 37 CFR1.57 and made a part of this specification.

BACKGROUND Field

The invention relates to the field of radiation therapy systems. Oneembodiment includes an active path planning and collision avoidancesystem to facilitate movement of objects in a radiation therapyenvironment in an efficient manner and so as to proactively avoidpossible collisions.

Description of Related Art

Radiation therapy systems are known and used to provide treatment topatients suffering a wide variety of conditions. Radiation therapy istypically used to kill or inhibit the growth of undesired tissue, suchas cancerous tissue. A determined quantity of high-energyelectromagnetic radiation and/or high-energy particles are directed intothe undesired tissue with the goal of damaging the undesired tissuewhile reducing unintentional damage to desired or healthy tissue throughwhich the radiation passes on its path to the undesired tissue.

Proton therapy has emerged as a particularly efficacious treatment for avariety of conditions. In proton therapy, positively charged protonsubatomic particles are accelerated, collimated into a tightly focusedbeam, and directed towards a designated target region within thepatient. Protons exhibit less lateral dispersion upon impact withpatient tissue than electromagnetic radiation or low mass electroncharged particles and can thus be more precisely aimed and deliveredalong a beam axis. Also, upon impact with patient tissue, protonsexhibit a characteristic Bragg peak wherein a significant portion of thekinetic energy of the accelerated mass is deposited within a relativelynarrow penetration depth within the patient. This offers the significantadvantage of reducing delivery of energy from the accelerated protonparticles to healthy tissue interposed between the target region and thedelivery nozzle of a proton therapy machine as well as to “downrange”tissue lying beyond the designated target region. Depending on theindications for a particular patient and their condition, delivery ofthe therapeutic proton beam may preferably take place from a pluralityof directions in multiple treatment fractions to maintain a total dosedelivered to the target region while reducing collateral exposure ofinterposed desired/healthy tissue.

Thus, a radiation therapy system, such as a proton beam therapy system,typically has provision for positioning a patient with respect to aproton beam in multiple orientations. In order to determine a preferredaiming point for the proton beam within the patient, the typicalprocedure has been to perform a computed tomography (CT) scan in aninitial planning or prescription stage from which multiple digitallyreconstructed radiographs (DRRs) can be determined. The DRRssynthetically represent the three dimensional data representative of theinternal physiological structure of the patient obtained from the CTscan in two dimensional views considered from multiple orientations. Adesired target isocenter corresponding to the tissue to which therapy isto be provided is designated. The spatial location of the targetisocenter can be referenced with respect to physiological structure ofthe patient (monuments) as indicated in the DRRs.

Upon subsequent setup for delivery of the radiation therapy, an x-rayimager is moved into an imaging position and a radiographic image istaken of the patient. This radiographic image is compared or registeredwith the DRRs with respect to the designated target isocenter. Thepatient's position is adjusted to, as closely as possible, align thetarget isocenter in a desired pose with respect to the radiation beam asindicated by the physician's prescription. The desired pose isfrequently chosen as that of the initial planning or prescription scan.Depending on the particular application, either the patient and/or thebeam nozzle will need to be moved.

There is a desire that movement of components of the therapy system toachieve alignment be done in an accurate, rapid manner while maintainingoverall system safety. In particular, a radiation therapy apparatus isan expensive piece of medical equipment to construct and maintain bothbecause of the materials and equipment needed in construction and theindication for relatively highly trained personnel to operate andmaintain the apparatus. In addition, radiation therapy, such as protontherapy, is increasing being found an effective treatment for a varietyof patient conditions and thus it is desirable to increase patientthroughput both to expand the availability of this beneficial treatmentto more patients in need of the same as well as reducing the end coststo the patients or insurance companies paying for the treatment andincrease the profitability for the therapy delivery providers. As theactual delivery of the radiation dose, once the patient is properlypositioned, is relatively quick, any additional latency in patientingress and egress from the therapy apparatus, imaging, and patientpositioning and registration detracts from the overall patientthroughput and thus the availability, costs, and profitability of thesystem.

The movable components of a radiation therapy system also tend to berather large and massive, thus indicating powered movement of thevarious components. As the components tend to have significant inertiaduring movement and are typically power driven, a safety system toinhibit damage and injury can be provided. Safety systems can includepower interrupts based on contact switches. The contact switches areactivated at motion stop range of motion limits to cut power to drivemotors. Hard motion stops or limiters can also be provided to physicallyimpede movement beyond a set range. However, contact switches and hardstops are activated when the corresponding component(s) reach the motionlimit and thus impose a relatively abrupt motion stop which adds to wearon the machinery and can even lead to damage if engaged excessively. Inaddition, particularly in application involving multiple movingcomponents, a motion stop arrangement of contact switches and/or hardlimiters involves significant complexity to inhibit collision betweenthe multiple components and can lead to inefficiencies in the overallsystem operation if the components are limited to moving one at a timeto simplify the collision avoidance.

From the foregoing it will be understood that there is a need forproviding a collision avoidance system to maintain operating safety anddamage control while positioning multiple movable components of aradiation therapy delivery system. There is also a desire to maintainthe accuracy and speed of the patient registration process whenimplementing such a collision avoidance system.

SUMMARY

Embodiments of the invention provide a patient positioning system for atherapeutic radiation system having moving components. The patientpositioning system pre-plans and analyzes movements to increase movementefficiency for decreased latency and to pro-actively avoid collisions.The patient positioning system includes multiple cameras that can bothdetermine the location of fixed and movable components of the system aswell as monitor for possible intrusion into a movement path of a foreignobject or personnel. The system provides significant safety advantagesover systems employing motion stops.

One embodiment comprises a radiation therapy delivery system havingfixed and movable components, the system comprising a gantry, a patientpod configured to secure a patient substantially immobile with respectto the patient pod, a patient positioner interconnected to the patientpod so as to position the patient pod along multiple translational androtational axes within the gantry, a radiation therapy nozzleinterconnected to the gantry and selectively delivering radiationtherapy along a beam axis, a plurality of external measurement deviceswhich obtain position measurements of at least the patient pod andnozzle, and a controller which receives the position measurements of atleast the patient pod and nozzle and determines movement commands toposition the patient in a desired pose with respect to the beam axis andcorresponding movement trajectories of the patient pod with respect toother fixed and movable components of the therapy delivery system basedupon the movement commands and determines whether a collision isindicated for the movement commands and inhibits movement if a collisionwould be indicated.

Another embodiment comprises a path planning and collision avoidancesystem for a radiation therapy system having fixed and movablecomponents and selectively delivering a radiation therapy beam along abeam axis, the positioning system comprising a plurality of externalmeasurement devices arranged to obtain position measurements of thecomponents so as to provide location information, a movable patientsupport configured to support a patient substantially fixed in positionwith respect to the patient support and controllably position thepatient in multiple translational and rotational axes, and a controllerreceiving position information from the plurality of externalmeasurement devices and providing movement commands to the movablepatient support to automatically align the patient in a desired pose anddetermining a corresponding movement envelope wherein the controllerevaluates the movement envelope and inhibits movement of the patientsupport if a collision is indicated else initiates the movement.

A further embodiment comprises a method of registering and positioning apatient for delivery of therapy with a system having fixed and at leastone movable components, the method comprising the steps of positioning apatient in an initial treatment pose with a controllable patientpositioner, externally measuring the location of selected points of thefixed and at least one movable components, determining a differencevector between the observed initial patient pose and a desired patientpose, determining corresponding movement commands and a movementtrajectory for the patient positioner to bring the patient to thedesired patient pose, and comparing the movement trajectory with themeasured locations of the selected points of the fixed and at least onemovable components so as to inhibit movement of the patient positionerif a collision is indicated.

Yet another embodiment comprises a system for delivering radiationtherapy to a pre-selected location within a patient, the systemcomprising a plurality of movable components including a patientpositioner and a nozzle, the system further comprising an externalmonitoring system that monitors the physical location of the pluralityof movable components and provides signals indicative thereof andwherein the system further includes internal monitoring systems thatalso monitor the movement of the plurality of movable components andprovides signals indicative thereof and wherein the system monitors thesignals from the external and internal monitoring systems and inhibitsmovement of the plurality of components if the signals indicate that acollision of components is likely to occur.

These and other objects and advantages of the invention will become moreapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A schematic diagram of one embodiment of a radiation therapy system witha patient positioning system in a first orientation is shown in FIG. 1Aand in a second orientation in FIG. 1B;

FIG. 2A illustrates one embodiment of retractable imagers in an extendedposition and FIG. 2B illustrates the imagers in a retracted position;

FIG. 3 illustrates one embodiment of a patient positioner to which apatient pod can be attached;

FIGS. 4A-4E illustrate various position error sources of one embodimentof a radiation therapy system;

FIG. 5 is a flow chart of one embodiment of a method f determining theposition and orientation of objects in a radiation therapy environment;

FIG. 6 illustrates one embodiment of external measurement devices for aradiation therapy system;

FIG. 7 illustrates further embodiments of external measurement devicesfor a radiation therapy system;

FIG. 8 is a block diagram of one embodiment of a precision patientpositioning system of a radiation therapy system;

FIG. 9 is a block diagram of one embodiment of an external measurementand 6D coordination system of the patient positioning system;

FIG. 10 is a block diagram of a patient registration module of thepatient positioning system;

FIG. 11 is a block diagram of a path planning module of a motion controlmodule of the patient positioning system;

FIG. 12 is a block diagram of an active collision avoidance module ofthe motion control module of the patient positioning system;

FIG. 13 is a block diagram of one embodiment of the collision avoidancemodule and a motion sequence coordinator of a motion control module; and

FIG. 14 is a flow chart of the operation of one embodiment of a methodof positioning a patient and delivering radiation therapy.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Reference will now be made to the drawings wherein like referencedesignators refer to like parts throughout. FIGS. 1A and 1B illustrateschematically first and second orientations of one embodiment of aradiation therapy system 100, such as based on the proton therapy systemcurrently in use at Loma Linda University Medical Center in Loma Linda,Calif. and as described in U.S. Pat. No. 4,870,287 of Sep. 26, 1989which is incorporated herein in its entirety by reference. The radiationtherapy system 100 is designed to deliver therapeutic radiation doses toa target region within a patient for treatment of malignancies or otherconditions from one or more angles or orientations with respect to thepatient. The system 100 includes a gantry 102 which includes a generallyhemispherical or frustoconical support frame for attachment and supportof other components of the radiation therapy system 100. Additionaldetails on the structure and operation of embodiments of the gantry 102may be found in U.S. Pat. Nos. 4,917,344 and 5,039,057, both of whichare incorporated herein in their entirety by reference.

The system 100 also comprises a nozzle 104 which is attached andsupported by the gantry 102 such that the gantry 102 and nozzle 104 mayrevolve relatively precisely about a gantry isocenter 120, but subjectto corkscrew, sag, and other distortions from nominal. The system 100also comprises a radiation source 106 delivering a radiation beam alonga radiation beam axis 140, such as a beam of accelerated protons. Theradiation beam passes through and is shaped by an aperture 110 to definea therapeutic beam delivered along a delivery axis 142. The aperture 110is positioned on the distal end of the nozzle 104 and the aperture 110may preferably be specifically configured for a patient's particularprescription of therapeutic radiation therapy. In certain applications,multiple apertures 110 are provided for different treatment fractions.

The system 100 also comprises one or more imagers 112 which, in thisembodiment, are retractable with respect to the gantry 102 between anextended position as illustrated in FIG. 2A and a retracted position asillustrated in FIG. 2B. The imager 112 in one implementation comprises acommercially available solid-state amorphous silicon x-ray imager whichcan develop image information such as from incident x-ray radiation thathas passed through a patient's body. The retractable aspect of theimager 112 provides the advantage of withdrawing the imager screen fromthe delivery axis 142 of the radiation source 106 when the imager 112 isnot needed thereby providing additional clearance within the gantry 102enclosure as well as placing the imager 112 out of the path ofpotentially harmful emissions from the radiation source 106 therebyreducing the need for shielding to be provided to the imager 112.

The system 100 also comprises corresponding one or more x-ray sources130 which selectively emit appropriate x-ray radiation along one or morex-ray source axes 144 so as to pass through interposed patient tissue togenerate a radiographic image of the interposed materials via the imager112. The particular energy, dose, duration, and other exposureparameters preferably employed by the x-ray source(s) 130 for imagingand the radiation source 106 for therapy will vary in differentapplications and will be readily understood and determined by one ofordinary skill in the art.

In this embodiment, at least one of the x-ray sources 130 ispositionable such that the x-ray source axis 144 can be positioned so asto be nominally coincident with the delivery axis 142. This embodimentprovides the advantage of developing a patient image for registrationfrom a perspective which is nominally identical to a treatmentperspective. This embodiment also includes the aspect that a firstimager 112 and x-ray source 130 pair and a second imager 112 and x-raysource 130 pair are arranged substantially orthogonal to each other.This embodiment provides the advantage of being able to obtain patientimages in two orthogonal perspectives to increase registration accuracyas will be described in greater detail below. The imaging system can besimilar to the systems described in U.S. Pat. Nos. 5,825,845 and5,117,829 which are hereby incorporated by reference.

The system 100 also comprises a patient positioner 114 (FIG. 3) and apatient pod 116 which is attached to a distal or working end of thepatient positioner 114. The patient positioner 114 is adapted to, uponreceipt of appropriate movement commands, position the patient pod 116in multiple translational and rotational axes and preferably is capableof positioning the patient pod 116 in three orthogonal translationalaxes as well as three orthogonal rotational axes so as to provide a fullsix degree freedom of motion to placement of the patient pod 116.

The patient pod 116 is configured to hold a patient securely in place inthe patient pod 116 so to as substantially inhibit any relative movementof the patient with respect to the patient pod 116. In variousembodiments, the patient pod 116 comprises expandable foam, bite blocks,and/or fitted facemasks as immobilizing devices and/or materials. Thepatient pod 116 is also preferably configured to reduce difficultiesencountered when a treatment fraction indicates delivery at an edge ortransition region of the patient pod 116. Additional details ofpreferred embodiments of the patient positioner 114 and patient pod 116can be found in the commonly assigned application (serial number10/917,022) entitled “Modular Patient Support System” filed concurrentlyherewith and which is incorporated herein in its entirety by reference.

As previously mentioned, in certain applications of the system 100,accurate relative positioning and orientation of the therapeutic beamdelivery axis 142 provided by the radiation source 106 with targettissue within the patient as supported by the patient pod 116 andpatient positioner 114 is an important goal of the system 100, such aswhen comprising a proton beam therapy system. However, as previouslymentioned, the various components of the system 100, such as the gantry102, the nozzle 104, radiation source 106, the imager(s) 112, thepatient positioner 114, the patient pod 116, and x-ray source(s) 130 aresubject to certain amounts of structural flex and movement tolerancesfrom a nominal position and orientation which can affect accuratedelivery of the beam to that patient.

FIGS. 1A and 1B illustrate different arrangements of certain componentsof the system 100 and indicate by the broken arrows both translationaland rotational deviations from nominal that can occur in the system 100.For example, in the embodiment shown in FIG. 1A, the nozzle 104 andfirst imager 112 extend substantially horizontally and are subject tobending due to gravity, particularly at their respective distal ends.The second imager 112 is arranged substantially vertically and is notsubject to the horizontal bending of the first imager 112. FIG. 1Billustrates the system 100 in a different arrangement rotatedapproximately 45° counterclockwise from the orientation of FIG. 1A. Inthis orientation, both of the imagers 112 as well as the nozzle 104 aresubject to bending under gravity, but to a different degree than in theorientation illustrated in FIG. 1A. The movement of the gantry 102between different orientations, such as is illustrated in FIGS. 1A and1B also subjects components of the system 100 to mechanical tolerancesat the moving surfaces. As these deviations from nominal are at leastpartially unpredictable, non-repeatable, and additive, correcting forthe deviations on a predictive basis is extremely challenging and limitsoverall alignment accuracy. It will be appreciated that these deviationsfrom the nominal orientation of the system are simply exemplary and thatany of a number of sources of error can be addressed by the systemdisclosed herein without departing from the spirit of the presentinvention.

FIGS. 4a-4e illustrate in greater detail embodiments of potentialuncertainties or errors which can present themselves upon procedures foralignment of, for example, the nozzle 104 and the target tissue of thepatient at an isocenter 120. FIGS. 4a-4e illustrate these sources ofuncertainty or error with reference to certain distances and positions.It will be appreciated that the sources of error described are simplyillustrative of the types of errors addressed by the system 100 of theillustrated embodiments and that the system 100 described is capable ofaddressing additional errors. In this embodiment, a distance SAD isdefined as a source to axis distance from the radiation source 106 tothe rotation axis of the gantry, which ideally passes through theisocenter 120. For purposes of explanation and appreciation of relativescale and distances, in this embodiment, SAD is approximately equal to2.3 meters.

FIG. 4a illustrates that one of the potential sources of error is asource error where the true location of the radiation source 106 issubject to offset from a presumed or nominal location. In thisembodiment, the therapeutic radiation beam as provided by the radiationsource 106 passes through two transmission ion chambers (TIC) whichserve to center the beam. These are indicated as TIC 1 and TIC 3 andthese are also affixed to the nozzle 104. The source error can arisefrom numerous sources including movement of the beam as observed on TIC1 and/or TIC 3, error in the true gantry 102 rotational angle, and errordue to “egging” or distortion from round of the gantry 102 as itrotates. FIG. 4a illustrates source error comprising an offset of thetrue position of the radiation source 106 from a presumed or nominallocation and the propagation of the radiation beam across the SADdistance through the aperture 110 providing a corresponding error atisocenter 120.

FIG. 4b illustrates possible error caused by TIC location error, whereTIC 1, the radiation source 106, and TIC 3 are offset from an ideal beamaxis passing through the nominal gantry isocenter 120. As the errorsillustrated by FIGS. 4a and 4b are assumed random and uncorrelated, theycan be combined in quadrature and projected through an assumed nominalcenter of the aperture 110 to establish a total error contribution dueto radiation source 106 error projected to the isocenter 120. In thisembodiment, before corrective measures are taken (as described ingreater detail below), the radiation source error can range fromapproximately ±0.6 mm to ±0.4 mm.

FIG. 4c illustrates error or uncertainty due to position of the aperture110. The location of the radiation source 106 is assumed nominal;however, error or uncertainty is introduced both by tolerance stack-up,skew, and flex of the nozzle 104 as well as manufacturing tolerances ofthe aperture 110 itself. Again, as projected from the radiation source106 across the distance SAD to the nominal isocenter 120, a beamdelivery aiming point (BDAP) error is possible between a presumednominal BDAP and an actual BDAP. In this embodiment, this BDAP errorarising from error in the aperture 110 location ranges fromapproximately ±1.1 mm to ±1.5 mm.

The system 100 is also subject to error due to positioning of theimager(s) 112 as well as the x-ray source(s) 130 as illustrated in FIGS.4d and 4e . FIG. 4D illustrates the error due to uncertainty in theimager(s) 112 position with the position of the corresponding x-raysource(s) 130 assumed nominal. As the emissions from the x-ray source130 pass through the patient assumed located substantially at isocenter120 and onward to the imager 112, this distance may be different thanthe SAD distance and in this embodiment is approximately equal to 2.2meters. Error or uncertainty in the true position of an imager 112 canarise from lateral shifts in the true position of the imager 112, errorsdue to axial shifting of the imager 112 with respect to thecorresponding x-ray source 130, as well as errors in registration ofimages obtained by imager 112 to the DRRs. In this embodiment, beforecorrection, the errors due to each imager 112 are approximately ±0.7 mm.

Similarly, FIG. 4e illustrates errors due to uncertainty in positioningof the x-ray source(s) 130 with the position of the correspondingimager(s) 112 assumed nominal. Possible sources of error due to thex-ray source 130 include errors due to initial alignment of the x-raysource 130, errors arising from movement of the x-ray source 130 intoand out of the beam line, and errors due to interpretation of sags andrelative distances of TIC 1 and TIC 3, These errors are also assumedrandom and uncorrelated or independent and are thus added in quadratureresulting, in this embodiment, in error due to each x-ray source 130 ofapproximately ±0.7 mm.

As these errors are random and independent and uncorrelated and thuspotentially additive, in this embodiment the system 100 also comprises aplurality of external measurement devices 124 to evaluate and facilitatecompensating for these errors. In one embodiment, the system 100 alsocomprises monuments, such as markers 122, cooperating with the externalmeasurement devices 124 as shown in FIGS. 2A, 2B, 6 and 7. The externalmeasurement devices 124 each obtain measurement information about thethree-dimensional position in space of one or more components of thesystem 100 as indicated by the monuments as well as one or more fixedlandmarks 132 also referred to herein as the “world” 132.

In this embodiment, the external measurement devices 124 comprisecommercially available cameras, such as CMOS digital cameras withmegapixel resolution and frame rates of 200-1000 Hz, which independentlyobtain optical images of objects within a field of view 126, which inthis embodiment is approximately 85° horizontally and 70° vertically.The external measurement devices 124 comprising digital cameras arecommercially available, for example as components of the Vicon Trackersystem from Vicon Motion Systems Inc. of Lake Forrest, Calif. However,in other embodiments, the external measurement devices 124 can compriselaser measurement devices and/or radio location devices in addition toor as an alternative to the optical cameras of this embodiment.

In this embodiment, the markers 122 comprise spherical, highlyreflective landmarks which are fixed to various components of the system100. In this embodiment, at least three markers 122 are fixed to eachcomponent of the system 100 of interest and are preferably placedasymmetrically, e.g. not equidistant from a centerline nor evenly oncorners, about the object. The external measurement devices 124 arearranged such that at least two external measurement devices 124 have agiven component of the system 100 and the corresponding markers 122 intheir field of view and in one embodiment a total of ten externalmeasurement devices 124 are provided. This aspect provides the abilityto provide binocular vision to the system 100 to enable the system 100to more accurately determine the location and orientation of componentsof the system 100. The markers 122 are provided to facilitaterecognition and precise determination of the position and orientation ofthe objects to which the markers 122 are affixed, however in otherembodiments, the system 100 employs the external measurement devices 124to obtain position information based on monuments comprisingcharacteristic outer contours of objects, such as edges or corners,comprising the system 100 without use of the external markers 122.

FIG. 5 illustrates one embodiment of determining the spatial positionand angular orientation of a component of the system 100. As thecomponent(s) of interest can be the gantry 102, nozzle 104, aperture110, imager 112, world 132 or other components, reference will be madeto a generic “object”. It will be appreciated that the process describedfor the object can proceed in parallel or in a series manner formultiple objects. Following a start state, in state 150 the system 100calibrates the multiple external measurement devices 124 with respect toeach other and the world 132. In the calibration state, the system 100determines the spatial position and angular orientation of each externalmeasurement device 124. The system 100 also determines the location ofthe world 132 which can be defined by a dedicated L-frame and can definea spatial origin or frame-of-reference of the system 100. The world 132can, of course, comprise any component or structure that issubstantially fixed within the field of view of the external measurementdevices 124. Hence, structures that are not likely to move or deflect asa result of the system 100 can comprise the world 132 or point ofreference for the external measurement devices 124.

A wand, which can include one or more markers 122 is moved within thefields of view 126 of the external measurement devices 124. As theexternal measurement devices 124 are arranged such that multipleexternal measurement devices 124 (in this embodiment at least two) havean object in the active area of the system 100 in their field of view126 at any given time, the system 100 correlates the independentlyprovided location and orientation information from each externalmeasurement device 124 and determines corrective factors such that themultiple external measurement devices 124 provide independent locationand orientation information that is in agreement following calibration.The particular mathematical steps to calibrate the external measurementdevices 124 are dependent on their number, relative spacing, geometricalorientations to each other and the world 132, as well as the coordinatesystem used and can vary among particular applications, however will beunderstood by one of ordinary skill in the art. It will also beappreciated that in certain applications, the calibration state 150would need to be repeated if one or more of the external measurementdevices 124 or world 132 is moved following calibration.

Following the calibration state 150, in state 152 multiple externalmeasurement devices 124 obtain an image of the object(s) of interest.From the images obtained in state 152, the system 100 determines acorresponding direction vector 155 to the object from each correspondingexternal measurement device 124 which images the object in state 154.This is illustrated in FIG. 6 as vectors 155 a-d corresponding to theexternal measurement devices 124 a-d which have the object in theirrespective fields of view 126. Then, in state 156, the system 100calculates the point in space where the vectors 155 (FIG. 6) determinedin state 154 intersect. State 156 thus returns a three-dimensionallocation in space, with reference to the world 132, for the objectcorresponding to multiple vectors intersecting at the location. As theobject has been provided with three or more movements or markers 122,the system 100 can also determine the three-dimensional angularorientation of the object by evaluating the relative locations of theindividual markers 122 associated with the object. In thisimplementation, the external measurement devices 124 comprise cameras,however, any of a number of different devices can be used to image,e.g., determine the location, of the monuments without departing fromthe spirit of the present invention. In particular, devices that emit orreceive electromagnetic or audio energy including visible andnon-visible wavelength energy and ultra-sound can be used to image ordetermine the location of the monuments.

The location and orientation information determined for the object isprovided in state 160 for use in the system 100 as described in greaterdetail below. In one embodiment, the calibration state 150 can beperformed within approximately one minute and allows the system 100 todetermine the object's location in states 152, 154, 156, and 160 towithin 0.1 mm and orientation to within 0.15° with a latency of no morethan 10 ms. As previously mentioned, in other embodiments, the externalmeasurement devices 124 can comprise laser measurement devices,radio-location devices or other devices that can determine direction toor distance from the external measurement devices 124 in addition to oras an alternative to the external measurement devices 124 describedabove. Thus, in certain embodiments a single external measurement device124 can determine both range and direction to the object to determinethe object location and orientation. In other embodiments, the externalmeasurement devices 124 provide only distance information to the objectand the object's location in space is determined by determining theintersection of multiple virtual spheres centered on the correspondingexternal measurement devices 124.

In certain embodiments, the system 100 also comprises one or more localposition feedback devices or resolvers 134 (See, e.g., FIG. 1). Thelocal feedback devices or resolvers 134 are embodied within or incommunication with one or more components of the system 100, such as thegantry 102, the nozzle 104, the radiation source 106, the aperture 110,the imager(s) 112, patient positioner 114, patient pod 116, and/or world132. The local feedback devices 134 provide independent positioninformation relating to the associated component of the system 100. Invarious embodiments, the local feedback devices 134 comprise rotaryencoders, linear encoders, servos, or other position indicators that arecommercially available and whose operation is well understood by one ofordinary skill in the art. The local feedback devices 134 provideindependent position information that can be utilized by the system 100in addition to the information provided by the external measurementdevices 124 to more accurately position the patient.

The system 100 also comprises, in this embodiment, a precision patientalignment system 200 which employs the location information provided instate 160 for the object(s). As illustrated in FIG. 8, the patientalignment system 200 comprises a command and control module 202communicating with a GD system 204, a patient registration module 206,data files 210, a motion control module 212, a safety module 214, and auser interface 216. The patient alignment system 200 employs locationinformation provided by the 6D system 204 to more accurately registerthe patient and move the nozzle 104 and the patient positioner 114 toachieve a desired treatment pose as indicated by the prescription forthe patient provided by the data files 210.

In this embodiment, the 6D system 204 receives position data from theexternal measurement devices 124 and from the resolvers 134 relating tothe current location of the nozzle 104, the aperture 110, the imager112, the patient positioner 114, and patient pod 116, as well as thelocation of one or more fixed landmarks 132 indicated in FIG. 9 as theworld 132. The fixed landmarks, or world, 132 provide a non-movingorigin or frame of reference to facilitate determination of the positionof the moving components of the radiation therapy system 100. Thislocation information is provided to a primary 6D position measurementsystem 220 which then uses the observed data from the externalmeasurement devices 124 and resolvers 134 to calculate position andorientation coordinates of these five components and origin in a firstreference frame. This position information is provided to a 6Dcoordination module 222 which comprises a coordinate transform module224 and an arbitration module 226. The coordinate transform module 224communicates with other modules of the patient alignment system 200,such as the command and control module 202 and the motion control withpath planning and collision avoidance module 212.

Depending on the stage of the patient registration and therapy deliveryprocess, other modules of the patient alignment system 200 can submitcalls to the 6D system 204 for a position request of the currentconfiguration of the radiation therapy system 100. Other modules of thepatient alignment system 200 can also provide calls to the 6D system 204such as a coordinate transform request. Such a request typically willinclude submission of location data in a given reference frame, anindication of the reference frame in which the data is submitted and adesired frame of reference which the calling module wishes to have theposition data transformed into. This coordinate transform request issubmitted to the coordinate transform module 224 which performs theappropriate calculations upon the submitted data in the given referenceframe and transforms the data into the desired frame of reference andreturns this to the calling module of the patient alignment system 200.

For example, the radiation therapy system 100 may determine thatmovement of the patient positioner 114 is indicated to correctlyregister the patient. For example, a translation of plus 2 mm along anx-axis, minus 1.5 mm along a y-axis, no change along a z-axis, and apositive 1° rotation about a vertical axis is indicated. This data wouldbe submitted to the coordinate transform module 224 which would thenoperate upon the data to return corresponding movement commands to thepatient positioner 114. The exact coordinate transformations will varyin specific implementations of the system 100 depending, for example, onthe exact configuration and dimensions of the patient positioner 114 andthe relative position of the patient positioner 114 with respect toother components of the system 100. However, such coordinate transformscan be readily determined by one of ordinary skill in the art for aparticular application.

The arbitration module 226 assists in operation of the motion controlmodule 212 by providing specific object position information uponreceipt of a position request. A secondary position measurement system230 provides an alternative or backup position measurement function forthe various components of the radiation therapy system 100. In oneembodiment, the secondary position measurement system 230 comprises aconventional positioning functionality employing predicted positioninformation based on an initial position and commanded moves. In oneembodiment, the primary position measurement system 220 receivesinformation from the external measurement devices 124 and the secondaryposition measurement system 230 receives independent positioninformation from the resolvers 134. It will generally be preferred thatthe 6D measurement system 220 operate as the primary positioning systemfor the previously described advantages of positioning accuracy andspeed.

FIG. 10 illustrates in greater detail the patient registration module206 of the patient alignment system 200. As previously described, the 6Dsystem 204 obtains location measurements of various components of theradiation therapy system 100, including the table or patient pod 116 andthe nozzle 104 and determines position coordinates of these variouscomponents and presents them in a desired frame of reference. The datafiles 210 provide information relating to the patient's treatmentprescription, including the treatment plan and CT data previouslyobtained at a planning or prescription session. This patient's data canbe configured by a data converter 232 to present the data in a preferredformat. The imager 112 also provides location information to the 6Dsystem 204 as well as to an image capture module 236. The image capturemodule 236 receives raw image data from the imager 112 and processesthis data, such as with filtering, exposure correction, scaling, andcropping to provide corrected image data to a registration algorithm241.

In this embodiment, the CT data undergoes an intermediate processingstep via a transgraph creation module 234 to transform the CT data intotransgraphs which are provided to the registration algorithm 241. Thetransgraphs are an intermediate data representation and increase thespeed of generation of DRRs. The registration algorithm 241 uses thetransgraphs, the treatment plan, the current object position dataprovided by the 6D system 204 and the corrected image data from theimager(s) 112 to determine a registered pose which information isprovided to the command and control module 202. The registrationalgorithm 241 attempts to match either as closely as possible or towithin a designated tolerance the corrected image data from the imager112 with an appropriate DRR to establish a desired pose or to registerthe patient. The command and control module 202 can evaluate the currentregistered pose and provide commands or requests to induce movement ofone or more of the components of the radiation therapy system 100 toachieve this desired pose. Additional details for a suitableregistration algorithm may be found in the published doctoraldissertation of David A. LaRose of May 2001 submitted to Carnegie MellonUniversity entitled “Iterative X-ray/CT Registration Using AcceleratedVolume Rendering” which is incorporated herein in its entirety byreference.

FIGS. 11-13 illustrate embodiments with which the system 100 performsthis movement. FIG. 11 illustrates that the command and control module202 has provided a call for movement of one or more of the components ofthe radiation therapy system 100. In state 238, the motion controlmodule 212 retrieves a current position configuration from the 6D system204 and provides this with the newly requested position configuration toa path planning module 240. The path planning module 240 comprises alibrary of three-dimensional model data which represent positionenvelopes defined by possible movement of the various components of theradiation therapy system 100. For example, as previously described, theimager 112 is retractable and a 3D model data module 242 indicates theenvelope or volume in space through which the imager 112 can movedepending on its present and end locations.

The path planning module 240 also comprises an object movement simulator244 which receives data from the 3D model data module 242 and cancalculate movement simulations for the various components of theradiation therapy system 100 based upon this data. This object movementsimulation module 244 preferably works in concert with a collisionavoidance module 270 as illustrated in FIG. 12. FIG. 12 againillustrates one embodiment of the operation of the 6D system 204 whichin this embodiment obtains location measurements of the aperture 110,imager 112, nozzle 104, patient positioner and patient pod 114 and 116as well as the fixed landmarks or world 132. FIG. 12 also illustratesthat, in this embodiment, local feedback is gathered from resolvers 134corresponding to the patient positioner 114, the nozzle 104, the imager112, and the angle of the gantry 102.

This position information is provided to the collision avoidance module270 which gathers the object information in an object position datalibrary 272. This object data is provided to a decision module 274 whichevaluates whether the data is verifiable. In certain embodiments, theevaluation of the module 274 can investigate possible inconsistencies orconflicts with the object position data from the library 272 such asout-of-range data or data which indicates, for example, that multipleobjects are occupying the same location. If a conflict or out-of-rangecondition is determined, e.g., the result of the termination module 274is negative, a system halt is indicated in state 284 to inhibit furthermovement of components of the radiation therapy system 100 and furtherproceeds to a fault recovery state 286 where appropriate measures aretaken to recover or correct the fault or faults. Upon completion of thefault recovery state 286, a reset state 290 is performed followed by areturn to the data retrieval of the object position data library inmodule 272.

If the evaluation of state 274 is affirmative, a state 276 follows wherethe collision avoidance module 270 calculates relative distances alongcurrent and projected trajectories and provides this calculatedinformation to an evaluation state 280 which determines whether one ormore of the objects or components of the radiation therapy system 100are too close. If the evaluation of stage 280 is negative, e.g., thatthe current locations and projected trajectories do not present acollision hazard, a sleep or pause state 282 follows during whichmovement of the one or more components of the radiation therapy system100 is allowed to continue as indicated and proceeds to a recursivesequence through modules 272, 274, 276, 280, and 282 as indicated.

However, if the results of the evaluation state 280 are affirmative,e.g., that either one or more of the objects are too close or that theirprojected trajectories would bring them into collision, the system haltof state 284 is implemented with the fault recovery and reset states 286and 290, following as previously described. Thus, the collisionavoidance module 270 allows the radiation therapy system 100 toproactively evaluate both current and projected locations and movementtrajectories of movable components of the system 100 to mitigatepossible collisions before they occur or are even initiated. This isadvantageous over systems employing motion stops triggered, for example,by contact switches which halt motion upon activation of stop or contactswitches, which by themselves may be inadequate to prevent damage to themoving components which can be relatively large and massive havingsignificant inertia, or to prevent injury to a user or patient of thesystem.

Assuming that the object movement simulation module 244 as cooperatingwith the collision avoidance module 270 indicates that the indicatedmovements will not pose a collision risk, the actual movement commandsare forwarded to a motion sequence coordinator module 246 whichevaluates the indicated movement vectors of the one or more componentsof the radiation therapy system 100 and sequences these movements via,in this embodiment, five translation modules. In particular, thetranslation modules 250, 252, 254, 260, and 262 translate indicatedmovement vectors from a provided reference frame to a command referenceframe appropriate to the patient positioner 114, the gantry 102, thex-ray source 130, the imager 112, and the nozzle 104, respectively.

As previously mentioned, the various moveable components of theradiation therapy system 100 can assume different dimensions and besubject to different control parameters and the translation modules 250,252, 254, 260, and 262 interrelate or translate a motion vector in afirst frame of reference into the appropriate reference frame for thecorresponding component of the radiation therapy system 100. Forexample, in this embodiment the gantry 102 is capable of clockwise andcounterclockwise rotation about an axis whereas the patient positioner114 is positionable in six degrees of translational and rotationalmovement freedom and thus operates under a different frame of referencefor movement commands as compared to the gantry 102. By having theavailability of externally measured location information for the variouscomponents of the radiation therapy system 100, the motion sequencecoordinator module 246 can efficiently plan the movement of thesecomponents in a straightforward, efficient and safe manner.

FIG. 14 illustrates a workflow or method 300 of one embodiment ofoperation of the radiation therapy system 100 as provided with thepatient alignment system 200. From a start state 302, follows anidentification state 304 wherein the particular patient and treatmentportal to be provided is identified. This is followed by a treatmentprescription retrieval state 306 and the identification and treatmentprescription retrieval of states 304 and 306 can be performed via theuser interface 216 and accessing the data files of module 210. Thepatient is then moved to an imaging position in state 310 by enteringinto the patient pod 116 and actuation of the patient positioner 114 toposition the patient pod 116 securing the patient in the approximateposition for imaging. The gantry 102, imager(s) 112, and radiationsource(s) 130 are also moved to an imaging position in state 312 and instate 314 the x-ray imaging axis parameters are determined as previouslydescribed via the 6D system 204 employing the external measurementdevices 124, cooperating markers 122, and resolvers 134.

In state 316, a radiographic image of the patient is captured by theimager 112 and corrections can be applied as needed as previouslydescribed by the module 236. In this embodiment, two imagers 112 andcorresponding x-ray sources 130 are arranged substantiallyperpendicularly to each other. Thus, two independent radiographic imagesare obtained from orthogonal perspectives. This aspect provides morecomplete radiographic image information than from a single perspective.It will also be appreciated that in certain embodiments, multipleimaging of states 316 can be performed for additional data. Anevaluation is performed in state 320 to determine whether theradiographic image acquisition process is complete and the determinationof this decision results either in the negative case with continuationof the movement of state 312, the determination of state 314 and thecapture of state 316 as indicated or, when affirmative, followed bystate 322.

In state 322, external measurements are performed by the 6D system 204as previously described to determine the relative positions andorientations of the various components of the radiation therapy system100 via the patient registration module 206 as previously described. Instate 324, motion computations are made as indicated to properly alignthe patient in the desired pose.

While not necessarily required in each instance of treatment delivery,this embodiment illustrates that in state 326 some degree of gantry 102movement is indicated to position the gantry 102 in a treatment positionas well as movement of the patient, such as via the patient positioner114 in state 330 to position the patient in the indicated pose.Following these movements, state 332 again employs the 6D system 204 toexternally measure and in state 334 to compute and analyze the measuredposition to determine in state 336 whether the desired patient pose hasbeen achieved within the desired tolerance. If adequately accurateregistration and positioning of the patient has not yet been achieved,state 340 follows where a correction vector is computed and transformedinto the appropriate frame of reference for further movement of thegantry 102 and/or patient positioner 114. If the decision of state 336is affirmative, e.g., that the patient has been satisfactorilypositioned in the desired pose, the radiation therapy fraction isenabled in state 342 in accordance with the patient's prescription. Forcertain patient prescriptions, it will be understood that the treatmentsession may indicate multiple treatment fractions, such as treatmentfrom a plurality of orientations and that appropriate portions of themethod 300 may be iteratively repeated for multiple prescribed treatmentfractions. However, for simplicity of illustration, a single iterationis illustrated in FIG. 14. Thus, following the treatment delivery ofstate 342, a finished state 344 follows which may comprise thecompletion of treatment for that patient for the day or for a givenseries of treatments.

Thus, the radiation therapy system 100 with the patient alignment system200, by directly measuring movable components of the system 100, employsa measured feedback to more accurately determine and control thepositioning of these various components. A particular advantage of thesystem 100 is that the patient can be more accurately registered at atreatment delivery session than is possible with known systems andwithout an iterative sequence of radiographic imaging, repositioning ofthe patient, and subsequent radiographic imaging and data analysis. Thisoffers the significant advantage both of more accurately delivering thetherapeutic radiation, significantly decreasing the latency of theregistration, imaging and positioning processes and thus increasing thepossible patient throughput as well as reducing the exposure of thepatient to x-ray radiation during radiographic imaging by reducing theneed for multiple x-ray exposures during a treatment session.

Although the preferred embodiments of the present invention have shown,described and pointed out the fundamental novel features of theinvention as applied to those embodiments, it will be understood thatvarious omissions, substitutions and changes in the form of the detailof the device illustrated may be made by those skilled in the artwithout departing from the spirit of the present invention.Consequently, the scope of the invention should not be limited to theforegoing description but is to be defined by the appended claims.

The following is claimed:
 1. A radiation therapy system operable toselectively deliver radiation along a delivery axis from one or moreangles or orientations with respect to a beam delivery aiming pointcomprising: a radiation source operable to irradiate a radiation beamalong a radiation beam axis; a gantry operable to revolve relativelyprecisely about a gantry isocenter wherein the radiation source isattached and supported by the gantry; a nozzle attached and supported bythe gantry, wherein an aperture is positioned on the distal end of thenozzle and the radiation beam passes through and is shaped by theaperture; the gantry and the nozzle being responsive to receivedinstructions to be positioned relative to a nominal beam delivery aimingpoint subject to certain amounts of structural flex and movementtolerances from nominal positions and orientations; a camera systemoperable to obtain images of moveable components of the radiationtherapy system and process the obtained images to determine positionmeasurements of the gantry; and a control system operable to receive theposition measurements from the camera system and utilize the positionmeasurements to determine an offset between an actual location of theradiation source attached to the gantry and an expected location of theradiation source attached to the gantry positioned in accordance withthe received instructions, wherein the control system monitors theposition measurements from the camera system and signals from internalmonitoring systems and inhibits movement of the moveable components ifthe position measurements and the signals indicate that a collision ofthe moveable components is likely to occur.
 2. The radiation therapysystem of claim 1 wherein the internal monitoring systems comprise oneor more local position feedback devices selected from a group consistingof: rotary encoders, linear encoders and servos associated with one ormore of the moveable components of the radiation therapy system.
 3. Amonitoring system for monitoring a radiation therapy system havingmovable components operable to position a radiation source relative to anominal beam delivery aiming point in accordance with receivedinstructions, wherein the movable components of the radiation therapysystem are subject to certain amounts of structural flex and movementtolerances from nominal positions and orientations, the monitoringsystem comprising: a camera system operable to obtain images of moveablecomponents of the radiation therapy system and process the obtainedimages to determine position measurements of the moveable components ofthe monitored radiation therapy system positioning the radiation sourcerelative to a nominal beam delivery aiming point; internal monitoringsystems that also monitor the movement of moveable components of theradiation therapy system and provide signals indicative thereof; and acontrol system operable to receive position measurements from the camerasystem and utilize the position measurements to determine an offsetbetween an actual location of the radiation source and an expectedlocation of the radiation source positioned in accordance with thereceived instructions, wherein the control system monitors the positionmeasurements from the camera system and signals from the internalmonitoring systems and inhibits movement of the moveable components ifthe control system determines that a collision is likely to occur. 4.The monitoring system of claim 3 wherein the internal monitoring systemscomprise one or more local position feedback devices selected from agroup consisting of: rotary encoders, linear encoders and servosassociated with one or more of the moveable components of the radiationtherapy system.